Fabrication of sub-micron high electron mobility transistors (HEMTs) involves dry etch removal of GaAs from an underlying AlGaAs or InGaAs stop layer. The etch selectivity is achieved by formation of AlF3 on AlGaAs, or InCl3 and InF3 on InGaAs, which must be removed before processing can proceed. Wet chemical cleaning has difficulty in such a situation because of surface tension effects. We have investigated use of Electron Cyclotron Resonance (ECR) H2 or Ar discharges, or hexafluoroacetylacetone (HFAC) vapor, for in-situ dry etch cleaning of HEMTs exposed to low bias BCl3/SF6 discharges. The HFAC vapor can remove most of the remnant fluorine, but is effective only when the sample is heated above ∼250°C. This relatively high temperature is not compatible with in-situ cleaning of the etched device. Low-bias(−75V) sputter cleaning with an Ar discharge removes all remnant Cl and ∼40% of the F, but dc biases above -125V are required for complete cleaning, and this ion bombardment can lead to damage in the HEMT. ECR H2 discharge exposure is effective in removing all Cl- and F-related residues in a short period (∼5 mins) with low dc biases (−25 V) on the sample.

Wet chemical etching of AlGaAs layers using a dilute mixture of ammonium hydroxide and hydrogen peroxide is monitored in real-time using dynamic optical reflectivity (DOR). The AlGaAs layers were grown as a multilayer reflector stack by chemical beam epitaxy (CBE). The reflectivity of a normal incidence 3 mW, 670 nm semiconductor diode laser is monitored during the etching process and analysis of the DOR trace gives the etch rate for the different etchant concentrations used.

Carbon doping of GaAs and AlGaAs is easily carried out during chemical beam epitaxy by controlling the proportions of the precursors trimethylgallium and triethylgallium. The diffusion of C introduced at levels of up to 1020 cm−3, has been studied by SIMS and by TEM. In the latter case the destruction of short period GaAs-Al.3Ga.7As superlattices was monitored in order to assess the extent of diffusion after annealing at 800°C. The results confirm that C is quite a stable dopant. In addition, the destruction of the superlattices indicates that the diffusion mechanism of C involves group III sublattice sites.

GaAs samples doped with Si to a concentration of ∼2.7×10 18cm−3 were annealed at temperatures between 800 and 1000°C for 3 to 20 hours under As-rich and As-poor conditions for Si outdiffusion which were then measured using the capacitance-voltage method employing an electrochemical profiler. The deduced Si diffusivity showed strong dependencies on the As4 vapor phase pressure, PAs4 and on the electron concentration, n. When reduced to that under intrinsic conditions, activation enthalpies of 3.91 eV and 4.19 eV were obtained for As-rich and As-poor annealing cases, respectively. From these results, it is concluded that Si outdiffusion in GaAs is governed by the triply-negatively-charged Ga vacancies, .

A new reactor for studying the purely homogeneous thermal decomposition of organometallic precursors used in the Metalorganic Vapor Phase Epitaxy (MOVPE) of semiconductors is presented. The idea is based on the use of a counterflow jet configuration with one jet being heated and the other unheated. The heated jet contains pure carrier gas (typically hydrogen or nitrogen), while the unheated jet contains vapors of an organometallic species diluted in the same carrier gas. Under appropriate operating conditions, decomposition of the organometallic species takes place near the stagnation plane where the hot jet collides with the cool jet. Since the reactions occur in the gas phase and away from hot walls, purely homogeneous kinetics can be obtained. Such a counterflow jet reactor was designed for studying the thermal decomposition of tertiary-butyl-arsine (TBA), t-C4H9AsH2, a very promising precursor for MOVPE of GaAs films. Two-dimensional finite element simulations of transport phenomena and kinetics have been used to identify optimal operating conditions. An experimental system was constructed and capillary-sampled mass spectroscopy at the stagnation plane was used to study the thermal decomposition of TBA in nitrogen at a total pressure of 252 Torr. Gas-chromatography of the effluent gas stream was employed for positive identification of the hydrocarbon byproducts. The results indicate the existence of two major decomposition routes: (1) A low activation energy pathway producing isobutane AsH, and (2) a higher activation energy, β-hydride elimination pathway producing isobutene and arsine.

Three-dimensional parts are machined in silicon using laser-induced chlorine etching reactions. Structures are created directly from solid-modeling computer-aided-design/computer-aided-manufacturing software. Removal rates exceeding 2×104 and 105μm3/s, several orders of magnitude faster than electrodischarge machining methods, are achieved at 1-μm, and 15-μm x-y resolution, respectively. Laser-induced metallization of resulting structures as well as replication through compression molding have been demonstrated.

We describe pyrolytic laser assisted chemical vapor deposition of Al from dimethylethylamine-alane with 514 nm radiation from an Ar+ laser. Results from deposition on different substrates, including Pt, Au, W, and Si, provide insight into to thermal and nucleation effects in the laser writing process. High purity Al lines with resistivity close to bulk Al are reported for a range of operating conditions. The relationship between operating parameters and the resulting properties of the deposited lines is investigated. We also demonstrate a two-step fast writing process based on fast laser nucleation of lines followed by selective chemical vapor deposition of Al on the nucleated pattern.

The short (UV) wavelength and the large beam cross-section of excimer lasers are expected to permit high resolution projection patterning and, for this reason, excimer laser deposition of Cu from organometallic precursors appears to be an interesting alternative for metallization in ULSI circuits. Unfortunately, the photolytic decomposition of those precursors leads to strong carbon contamination of the deposits. However, the valence state of the Cu in such deposits is unknown. In this paper, the reduction of two Cu (II) compounds, Cu(hmac)2 and Cu(hfac)2, under excimer laser irradiation in a hydrogen ambient is discussed. It is shown, with X-ray Photoelectron Spectroscopy, that, under our experimental conditions, Cu(hmac)2 is reduced to a Cu (I) compound while some of the Cu(hfac)2 appears to be reduced to the metallic state. Furthermore, reaction of the SiO2 substrate with the carbon from the Cu(hmac)2 precursor is observed.

It has been demonstrated that copper can be selectively deposited on a variety of substrates including Teflon (polytetrafluroethylene or PTFE), Kapton (polyimide resin), silicon and gallium arsnide from solution by photo-assisted initiated deposition. A copper containing solution was prepared from a mixture of copper(I) chloride (Cu2Ci2) and decaborane (B10H14) in diethyl ether and/or THF (tetrahydrofuran). The copper films were fabricated by ultraviolet photolytic decomposition of copper chloride and polyhedral borane clusters. This liquid phase deposition has a gas-phase cluster analog that also results in copper deposition via pyrolysis. The approach of depositing metal thin films selectively by pholysis from solution is a novel and an underutilized approach to selective area deposition.

We have studied laser-CVD of W on GaAs by X-ray Photoelectron Spectroscopy (XPS). Deposition of W is obtained by irradiating GaAs samples with a KrF excimer laser at normal incidence to the substrate, in a cell containing WF6 mixed with H2 and Ar. We have previously shown that WF6 and GaAs react at room temperature even without laser illumination. GaF3 formation and a loss of As were detected at the surface of the samples by XPS. At laser fluences of 50mJ/cm2, this reaction appears to be enhanced by laser heating of the substrate, but no metallic W is formed. At laser fluences of 67 mJ/cm2, metallic W begins to be deposited, through a pyrolytic dissociation reaction with the substrate.

The identification and repair of defects in flat panel displays (FPD's), most especially liquid crystal, are required to achieve acceptable manufacturing yields and reasonable costs. Laser cutting and laser direct writing, from gas phase reactants, are used to repair opens and shorts in conductor lines of FPD substrates (the LI laser repair system). This paper details platinum, copper and aluminum deposition processes including deposition parameters, conductivity data, Auger evaluations and microscopy characterizations. Life-study data on repaired, fully assembled FPD's will be presented. Also the laser direct-writing process for aluminum oxide, used to repair dielectric defects and to passivate metal repairs, will be described. Finally, a unique, localized vacuum system (SPOT VAC™ ), specifically engineered for laser deposition on large (500 × 500mm) flat substrates, will be detailed.

Selected covalent metal nitrides with limited thermal stability, such as Sn3N4, Cu3 N, and Ni3N, were prepared in a glow discharge system by reactive sputtering in a nitrogen plasma. These compounds were characterized by chemical analysis and their thermal behavior established by temperature-programmed thermal decomposition. These materials decompose into the elements with the rate reaching a maximum at 615, 465, and 405 °C for Sn, Cu, and Ni respectively. The feasibility of using these coatings to generate metal lines by maskJess laser writing was explored. Conductingmetal lines, a few micron in width, could be generated with each of these nitrides. The resistivities of the metal lines were within an order of magnitude of those of the bulk metals for Cu and Ni and somewhat more for Sn.

A laser direct writing system has been developed for low temperature deposition of WSix on TiN from a gas mixture of WF6 and SiH4-. An Ar+ laser (488 nm, 1.5 W) and a diode laser (796 nm, 1.0 W) are used as photon sources. Lines are written at scan speeds of up to 100 μ/s from a flowing gas mixture of WF6 and SiH4 diluted in Ar. Lines 1.5 to 11 nm wide and 20 to 180 nmthick are obtained at a writing speed of 100 μ/s with the Ar+ laser. Lines written using the diode laser are typically 4 to 12 μm wide and 160 to 860 nm thick. W/Si ratio in the deposits, as measured by Auger electron spectroscopy (AES), isbetween 1.5 and 1.8.

Surface analysis of the interaction of this gas mixture with the TiN surface without laser irradiation shows that W, Si and F are adsorbed on the surface when exposed simultaneously to WF6 and SiH4 producing an adsorbed layer where W/Si ratio is 1.3 and F/W ratio 1.7.

A selective deposition of W(Zn) metallization, for formation of diffused ohmic contacts onto InP-based material was realized by means of rapid thermal, low pressure metalorganic chemical vapor deposition (RT-LPMOCVD). The W(Zn) layers were deposited using a reactive gas mixture that contained diethylzinc (DEZn), WF6, H2 and Ar, at temperatures of 450 to 550°C and pressures in the range of 1–5 torr. Uniform andcontinuous layers of W(Zn), 30 to 120 nm thick, were obtained. These layers contained Zn at concentrations higher than 1×l018 cm−3, which was subsequentially in-diffused into the underlying semiconductor layer to form highly doped semiconductor layers as thick as 0.2μm. As a result, the specific contact resistance of the W(Zn)/ In0.53Ga0.47 As contact was reduced to minimum value of 5×l0−6 Ω·cm2. The W(Zn) film were found to be mechanically stable with a small compressive stress of 5.10−8 dyne. cm−2, and dry etch rates of up to 90 nmmin.

Chemical vapor deposition of metals is becoming a desirable alternative to physical deposition techniques (e.g. sputtering, evaporation) for applications in chip wiring. This is due to the possibility of achieving highly conformal coverage and low processing temperatures. Additionally, it is convenient to be able to enhance the physical properties (e.g. corrosion resistance, adhesion, electromigration resistance) of metal films used for chip interconnection by incorporation of an alloying agent. We have investigated the possibility of extending our current copper deposition process to allow for the deposition of copper alloys. By careful selection of the precursors and reactor conditions, simultaneous decomposition of the two compounds to give clean alloy films is effected. Using this co-deposition method, Cu-Co and Cu-Te alloy films were prepared. Precursor and reaction chemistry are discussed as well as some properties of the resulting films.

We report a highly reliable, sputtered WGe emitter contact for npn heterojunction bipolartransistors. A specific contact resistance of 7.5 × 10−7 Ω-cm2 and a transfer resistance of 4.0 × 10−2 Ωmm were obtained after 380°C, 1 min alloy. The contact was patterned by SF6 dry etching at low bias using a Au mask. This novel contact has comparable resistance to conventional AuGe-based metallization while having superior thermal stability. We have studied the dependence of contact properties on the post-deposition annealing conditions by transfer length method of electrical characterization and Auger analysis, and will also report long-term reliability results in comparison to AuGe-based metallization.

Transition metal-germanide/silicide based ohmic contact systems to n-type GaAs have been studied using current-voltage (I-V) and transmission line measurements (TLM). The effects of substituting various metals from groups IVB and VIB into the metallization stack have been compared, as well as the effects of using germanium or silicon. Rapid Thermal Annealing (RTA) was used to facilitate the reactions. Titanium and molybdenum were shown to be more effective metallizations than chromium, even though chromium readily forms a silicide or germanide. Germanium has been found to produce an ohmic contact of low resistivity, while metallization with silicon alone does not show ohmic behavior.

Thermal stability of the Schottky contacts on Ga0.51In0.49P has been made. The Ga0.51In0.49P epitaxial layer was successfully grown on the GaAs substrate by LP-MOCVD to form a lattice-matched heterostructure. In this paper, materials aspects of the Ga0.51In0.49P layers were characterized and thermal stability of three different types of films, including single-layer metal (Pt, Ni, Pd, Au, Co, Mo, W, Cr, Ti, Al, Ta, and In), metal silicides (WSi2, W5Si3, PtSi, and Pt2i), and TiW nitrides (TiWNx ) as the Schottky contacts materials on Ga0.51In0.49P were studied. Due to the high bandgap nature of Ga0.51In0.49P, the Schottky contacts on Ga0.51In0.49P demonstrate good characteristics. The barrier heights range from 0.79 to 1.19 eV depending on the selection of the materials and the annealing conditions. For single-metal contacts, Pt film shows the best thermal stability, the barrier height of 1.09 eV and the ideality factor of 1.06 were obtained for the Pt Schottky diode with furnace annealing at 500 °C for 30 min. For refractory compound films, the TiWNx film shows the best thermal stability. The TiWNx Schottky contacts demonstrate excellent electrical as well as physical characteristics, even after high temperature annealing at 850°C.

A tri-level resist scheme using low temperature (<50°C) deposited SiNx ratfier than Ge for the transfer layer has been developed. This allows use of an optical stepper for lithographic patterning of the emitter-base junctions in GaAs/AlGaAs heterojunction bipolar transistors (HBTs) where a conventional lift-off process using a single level resist often leads to die presence of shorts between metallizations. The plasma-enhanced chemically vapor deposited (PECVD) SiNx shows a sligtly larger degree of Si-H bonding compared to nitride deposited at higher temperature (275°C), and is under compressive stress (-5 × 1010 dyne · cm−2) which is considerably relieved upor thermal cycling to 500°C (-1.5 × 1010 dyne · cm−2 after cool-down). This final stress is approximately a factor of two higher man conventional PECVD SiNx cycled in the same manner. The adhesion of the low temperature nitride to die underlying polydimediylglutarimide (PMGI) base layer in the tri-level resist is excellent, leading to high yields in the lift-off metallization process. These layers are etched in Electron Cyclotron Resonance (ECR) discharges of SF6 or O2, respectively, using low additional dc bias (≤-100V) on the sample. Subsequent deposition of the HBT base metallization (Ti/Ag/Au) and lift-off of the tri-level resist produces contacts with excellent edge definition and an absence of shorts between metallization.

A series of volatile heterodinuclear organometallic compounds of the general formula L(CO)nM-ER1R2(D) (L = CO, η5-C5H5, P(CH3)3; n = 1–4; M = Mn, Fe, Co, Ni; E = Al, Ga, In; R = H, alkyl; D = O- or N-donor ligand) was syndiesized and characterized. These compounds exist either as low melting solids or liquids with vapor pressures typically around 10–50 mTorr at room temperature. The possibility to grow bimetallic thin films ME (e.g. CoAl, CoGa, Coin, Niln etc.) from those single source molecular precursors by thermally induced low pressure OMCVD was investigated. It was shown that the thin film composition, namely the metal stoichiometry, can be controlled by the ligand set at the metal atoms.